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Uses an array of large antennas at the cell site to measure the angle of the incoming control signal from the handset. A minimum of two cell sites is required to determine location, and no handset modifications are needed. However, this solution requires capital expenditures by the carrier, particularly in remote areas. AOA accuracy is negatively impacted by line-of-sight obstacles and distance from the base station and may not function well in an urban environment.

Assisted GPS

By shifting much of the processing burden from the handset to the network, A-GPS helps to overcome some of the drawbacks of pure GPS such as cost, power consumption, speed to determine location, and the line-of-sight requirement. Additionally, the network keeps track of location so that when satellites are obstructed, a good estimate of location can be obtained based on the last reading. A-GPS is not costly (~$20) from a handset perspective but requires additional investment in the network, Location can usually be ascertained in about 5 seconds and A-GPS accuracy is considered the highest.

Authentication Center (AuC)

Database that keeps the authentication register of all subscribers. The mobile handset contains a key that must be authorized by the AuC for the handset to gain access to the network.

Average Revenue per User(ARPU)

Refers to the average monthly bill per subscriber.

Bandwidth

Breadth of the frequency used. Analogous to a water pipe, in which a larger diameter allows more water to be moved. Therefore, a 30-MHz wireless license to much more valuable, in terms of capacity and throughput, than a 15- or 10-MHz license.

Cell of Origin (COO)

System currently used to comply with Phase 1 E-911 requirements. This technology tells which cell a caller is occupying, but offers no greater resolution. Cell location can generally be ascertained in about 3 seconds. The accuracy of COO is determined by the teledensity of the area, with accuracy proportional to the number of cell sites, or size of the cell. This solution requires no alteration to the network or to the handsets, but is insufficient for emergency services.

Code Division Multiple Access (CDMA)

Spread-spectrum approach to digital transmission. This method of transmission assigns unique codes to each transmission and then transmits over the entire spectrum. The mobile phone is instructed to decipher only a particular code in order to receive the designated transmission. The assignment of separate codes allows multiple users to share the same air spare. CDMA increases capacity 8-20 times vs. analog cellular and also has greater capacity than TDMA.

Enhanced Cell ID (E-CID)

A software-based solution that determines location by comparing the list, or table, of cell sites available to the handset. Once the available cell sites are known (this is constantly updated), location can be calculated based on the intersections of the overlapping cells. This system works best in areas with many cell sites, the location can be determined within about 100 meters (250 meters in rural areas). A key advantage of E-CID is that the line of sight is not required. Currently, this system only works with GSM networks. Because E-CID requires only slight modification to the SIM card in the handset and a proprietary network server it is regarded as a relatively low-cost and nondisruptive solution for GSM operators.

Enhanced Data Rates for GSM Evolution (EDGE)

An evolutionary path to 3G services for GSM and TDMA operators. It represents a merger of GSM and TDM A standards and builds on the GPRS air interface and networks. EDGE is a data-only upgrade and supports packet data at speeds up to 384 kbps. EDGE is able to achieve increased data transmission speeds trough a change in its modulation scheme, from GMSK to 8 PSK. Then upgrade to EDGE in relatively expensive and requires that carriers replace the transceivers (radio antennas) at every cells site. According to Commonwealth Associates, this scan cost as much as 60% of the original network cost.

Enhanced Observed Time Difference (E-OTD)

Operates under the same principles as TDOA (measuring the time it takes to receive a signal), but in reverse. This signals a received from at least three base stations, whose locations are known, and location is calculated by the handset. E-OTD utilizes the existing capabilities of the GSM protocol as is relatively straightforward to apply to these networks. E-OTD is a more costly and complex solution to deploy TDOA because of the handset software upgrades and location measurement units (reference beacons), but it yields much better location information. Location measurement units are distributed throughout the network, with about one unit for every four cell sites. Time keeping is of the utmost importance, and system time is usually kept by an atomic clock. E-OTD can usually provide location information accurate to 50-125 meters within 5 seconds. However, this system can be susceptible to distortion in urban areas.

Global Positioning System(GPS)

A world-wide radio navigation system comprised of 24 satellites and ground stations sponsored by the U.S. Department of Defense. The systems measures the longitude, latitude, and elevation of the receiver. Triangulation is used to determine location. This is accomplished by measuring the time it takes to communicate with 3 satellites. A fourth measurement is taken to ensure that the timing is the pseudorandom codes is synchronized. Because time is critical in the calculation of location, an atomic clock is used. This means that location cannot be determined if the user is inside a building, in an urban canyon, or under a heavy canopy of trees. To communicate with the satellites and to perform the complex calculations, GPS takes the most time of the location technologies to determine location, requiring 10-60 seconds.

Home Location Register (HLR)

Centralized database that stores information on all subscribers. The HLR also maintains location information about the subscriber.

Packet Switching

A packet-switched system transmits data in packets that are reassembled by the receiver, rather than by establishing a dedicated connection. This is the same method used by the Internet. Packet switching allows for an “always on” connection and a vast increase in capacity, since a dedicated circuit contains more bandwidth than is consumed by a voice call. Packet switching is a critical enabler for most of the data services currently being contemplated, and it allows for the “push” of information to the customer. Packet switched systems such as GPRS were being piloted in Europe in late 2000.

Subscriber Information

Removable cards that enable mobile users to customize their headsets and access to the services of carriers outside their home region. By inserting an SIM card into an appropriate mobile phone for a region, international travelers can access services from other operators. SIM cards can also contain personal information such as address books, phone numbers, and calendars. They can store account or credit card numbers securely and transfer them from phone to phone, thus enabling m-commerce.

Spectrum

Refers to the ability to transmit signals at a specific frequency and the bandwidth of the frequency.

Time Distance of Arrival (TDOA)

Uses at least three base stations to measure to compare the arrival time of the control signal from a mobile handset on order to calculate location. To accurately determine location, strict synchronization of the base stations is required. Synchronization is such a critical issue, that an atomic clock is used in each base station. This solution may be attractive to CDMA network, which are already synchronized, versus GSM network, which may be asynchronous. TDOA requires line of sight to determine location. This can present problems in rural areas, where three cell sites cannot be accessed simultaneously, and in urban canyons, where multipath reflection can be a problem. TDOA is also less accurate than E-OTD, Cell-ID, or GPS, and can take up to 10 seconds to determine location. TDOA antennas are less expense and easier to deploy than AOA antennas, and TDOA does not require and handset modifications. However, TDOA is still regarded as a fairly expensive location solution.

Time Division Multiple Access (TDMA)

Utilizes a scheme in which the transmission channel is broken into six time slots. Three of the time slots are used to carry information and three of the time slots are unused in order to minimize interference or noise. Work is currently being done to increase the number of time slots and thus capacity. TDMA increases capacity 3 to 5 times that of analog cellular.

Visitor Location Register (VLR)

Database that keeps a record of all mobile subscribers currently active in a particular MSC. The handset routinely sends signals to the VLR to alert the system to its presence. The VLR forwards this information back to the HLR so that calls can be properly routed to the handset.

Wireless Application Service Providers (WASPs)

Companies that host or provision applications in a wireless environment. This is a relatively new industry with new firms entering at a rapid pace. As a new industry, the boundaries are not well defined, and clear winners have not yet emerged. The services offered by firms in this market space include wireless web hosting, wireless web translation, information provision, mobile middleware, and enterprise-application hosting. These services are generally managed from a central location or network operation center.

Satellites and Orbits – Background and Context

It took 300 years to see that vision become a reality. And to date, there have been around 6,600 satellite launches, with approximately 3,600 satellites still in orbit. Of these only 1,071, or so, are fully functioning.

A Modern Telecommunications Satellite

Words like Low Earth Orbit and Geo Stationary Orbit are common expressions in the satellite and telecommunications communities. But what do they really mean?

Geosynchronous Orbit

This is where the period of rotation is not 24hrs but some multiple (or fraction) of 24hrs.

Such a satellite would pass over the same spot on the Earth at a given time (or times) each day. For example, a satellite in Equatorial Orbit with a period of rotation of 12hrs, would pass over the same spot twice each day.

Geostationary Orbit

Geostationary is a special case of “Geosynchronous orbit”.

In the 1940’s Arthur C Clarke, published an article in Wireless World. Clarke explained that a satellite orbiting the Earth at an altitude of 36,000 km above the equator would circle the Earth in exactly 24Hrs. Such a satellite would maintain a “geostationary position”. Thus, to observers on Earth, it would appear to remain motionless in the sky.

Of our 1071 satellites still functioning approximately 500 are in “Geostationary” or “Geosynchronous” orbit. I.E. around 36,000 km above our heads.

Medium Earth Orbits (MEO)

These are satellites orbiting at an altitude of between 10,000km and 20,000km. This distance places them between the Van Allen belts where radiation exposure is minimized. MEO’s are not necessarily limited circular orbits. We have approximately 50 satellites in MEO.

Low Earth Orbits (LEO)

Satellites such as the International Space Station (ISS), are in LEO. Typically, such orbits are 1000km or less and circular. This facilitates easy “re-visit” capability.

Low Earth Orbiting satellites have a relatively short period of rotation, usually of the order of 100 minutes or so. This means that they speed across the sky and disappear below the horizon quiet quickly. As such until recently they were thought inappropriate for Telecommunications. However, during the 1990’s a “constellation” of these satellites was deployed making them useful for telecommunications. (Eg: Iridium Satellite Constellation). There are approximately 500 satellites screaming across our sky in Low Earth Orbit at present.

And more recently Sir Richard Branson’s Virgin Galactic are investing heavily into Satellite Internet technologies, such as Halo-Fi.

You may recall my last blog outlining the relationship between exponential numbers, science and finance. (This has always been a fascination of mine – I mean, interest rates and satellite orbits?? Why?)

We’ll get to that in a minute. Let’s examine natural phenomena – Bacterial growth rates.

Bacteria reproduce by “binary fission”

Let’s assume a single bacterium is put in a jar at 11pm. The bacterium reproduces itself every minute, i.e. the number of bacteria in the jar doubles every minute. The number of bacteria increases in the sequence 1,2,4,8, etc. After 1 hour the jar is completely full….

I ask you at what minute is the jar half full?

That’s right – at 11:59 pm

And at 11:58 pm it is a quarter full.

And at the 11:57 pm it is an eighth full.

And so on, right back to the original bacterium.

Why is this important?

Well, interest rates work that way too! We all know that your money is unlikely to double every minute, but it will double. For example, at 10% your money will double every seven years. And this is easy to calculate…. Just divide 70 by your interest rate:

70/10 = 7 years

The math is based on the natural logarithm of 2 (ie doubling), and 100Ln 2 = 69. Whatever, use your calculator… but trust me its close enough to 70.

Another question…

At 11:58 pm, how many bacteria would have realized that they were running out of room?

And if you retire at age 65 and your money is invested at 10%, how old are you at 11:58pm?

Many of you would know I am a trained accountant. Most would not know that my original training was in science and engineering. It’s that aspect of my life the I would like to write about now.

All of you would however be familiar with the concept of interest rates. A nightly topic on the news, interest rates determine how much spare cash we have after the mortgage payment. And the total mortgage paid is a simple calculation. To save time, I’m going to skip the math… but the formula is:

FV = PV(1+r)^t

Where:

FV = Future value

PV = Present Value

r = Interest Rate

t = time

its the formula for calculating the total amount you pay – and, (just like me), its not very sexy!

This is sooo cool. A total solar eclipse is due on the 8th of march. The moon will pass in front of the Sun at 6pm AEST and a total eclipse will move north east through Indonesia, Papua New Guinea and Borneo.

At its widest the shadow will be 156Km wide and total darkness will last between 90 seconds and 4 minutes. (Plenty of time to cast your sacrificial virgin into the volcano!!)

Parts of Northern Australia will experience a partial eclipse. However you can experience the event Live via the following link. View Eclipse Live.

Also Solar Dynamics will post live images as the event takes place. Solar Dynamics is a really cool NASA site and I suggest you check it out anyway.

The Moon – the Earth’s first satellite

The subject of countless poems and love songs the moon is the Earths first ever satellite. And our first satellite is still our most beautiful and powerful. Rolling tides, and shaping weather across the globe the moon sustains life. However it is man-made satellites that are of interest here……